1. Field of the Invention
The present invention relates to a switched-mode power supply using a variable bias current.
2. Description of the Related Art
In general, a power supply such as an adapter or a switched-mode power supply (SMPS) includes a power switch for performing power conversion depending on a load condition using pulse width modulation (hereinafter referred to as “PWM”).
Typically, a power supply includes a power switch receiving a rectified input voltage to generate an output voltage of a level desired by a user by being switched on or off, and an operating circuit generating an operating signal for driving the power switch.
In existing power supplies, a PWM signal having a regular period is used as the driving signal for the power switch.
In such a power switch operated by such a PWM signal, switching noise may occur during switching, and devices around the power switch may be adversely affected.
Patent Document 1 relates to a switching control device, a power supply device comprising the same, and a switching control method. However, according to the disclosure in Patent Document 1, a bias current cannot be periodically varied; and, therefore, Patent Document 1 does not disclose the features of reducing switching noise and improving electromagnetic interference (hereinafter referred to as “EMI”) characteristics by varying a bias current.